This invention relates to a pneumatic three-position shift mechanism for use in vehicle transfer cases wherein the number of components to provide the shift mechanism is reduced compared to the prior art.
Vehicle transfer cases are typically provided with the ability to move a shift yoke between a first position at which is engages a low speed gear, a second position at which it engages a high speed gear, and a third intermediate neutral position at which neither gear is engaged. Typically, these systems have incorporated a shift rod that is movable within a two-part housing between the three positions. At one end of the shift rod are a pair of cylinders movable within three different chambers and between the several positions. At the opposed end of the shift rod is a guiding chamber in which the shift rod is movable.
In the prior art, all of the fluid chambers are provided by separate housings which are bolted to the main transfer case housings. With each separate housing, the number of seals and fluid tight connections that must be utilized increases. Thus, with the prior art, there are required seals and securing devices for separate fluid housings at each of the two ends of the transfer case.
FIG. 1 shows an example 20 of the prior art transfer case. A housing 22 has a split line 24 dividing two housings sub-portions 26 and 28. A shift rod 30 is received extending between the two, and moves a shift collar 32 to selectively engage one of the two gears 34 and 36. Gear 34 is a low speed and gear 36 is a high speed gear. The collar 32 is shown in the intermediate or neutral position.
A fluid cylinder 38 is bolted to one end of the housing 28. The other housing portion 26 receives the bolted on fluid housing 40. Housing 40 receives the rear end 42 of the shift rod 30 and housing 38 receives the forward end 44 which moves with a plurality of pistons to achieve the various positions of the collar 32.
As can be appreciated, with the separate housings 38 and 40 a good deal of additional attachments, seals, etc. are necessary.
In the disclosed embodiment of this invention, the chambers for receiving both the piston and preferably the remote end of the shift rod are formed by integral bores in the transfer case housings. In this way, the bores are self-sealed, and no separate sealing elements or elaborate fluid-type securing devices are necessary.
In a preferred embodiment of this invention, both of the chambers are formed by bores. The bore for receiving a remote end is preferably a blind bore extending into the housing. The bore for receiving the piston end of the shift rod is preferably a bore which opens outwardly through a plurality of stepped bore portions. One of the pistons is preferably of a larger diameter and is movable within a first stepped portion. An end cap is received with a second outer diameter stepped portion of the bore, and provides the outer end for the fluid cylinder. This cap is all that need be secured to the housing in a fluid tight manner. As can be appreciated, the present invention thus greatly reduces the number of required components.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.